The leaves are trigonal; they are very short, and they are laid over each other like scales in four rows.
Fig. 73 represents a crystal of tourmaline with the trigonal prism , hexagonal prism , and a trigonal pyramid at each end.
Trigonal trapezohedron (fig. 74), bounded by six trapezoidal faces.
All other forms, in which the faces are neither parallel nor perpendicular to the triad ...